Well, my friend dared me to try "namida sushi" (涙寿司). It means literally "tear sushi"because one bite will have you crying. I sure did. The only ingredient besides the rice filling is spicy wasabi! A decent amount of it, too. Usually only a small amount of wasabi is mixed with soy sauce. But occassionally some restaurants across Japan serve this strange food that has a lump of it raw right inside the sushi roll!
I have had a lot of different kinds... I think the most "exotic" was whale. I was out with co-workers and I have a policy of not asking what it is until I have tried it. That way I don't make any judgements ahead of time. It was part of the set menu so I just had it right off my plate.
I have had some weird flavor combos recently at my local kaiten zushi.